The present invention relates to a thermal transfer type multicolor printer and more specifically to a printing paper feed apparatus of a thermal transfer type multicolor printer, in which a multicolor printing is carried out by the use of a transfer ribbon which carries a plurality of heat-dissolving inks.
One of the inventors has proposed as a joint inventor thermal transfer type multicolor printers in U.S. Pat. No. 4,551,729 entitled METHOD OF MAKING THERMAL TRANSFER TYPE MULTICOLOR PRINTING and issued on Nov. 5, 1985. The disclosure of this patent is incorporated herein by reference. In the prior art printers, a thermal transfer type multicolor printing is xade while both a printing paper and an ink film, placed over the printing paper, are moved between a thermal head and a platen roller which has sprocket pins mounted to it. The ink film has a base film applied with yellow, magenta and cyan inks in turns. After printing of a picture component for a predetermined color, the printing paper is returned to an initial or home position and the ink film is advanced for subsequent printing in another color. Thus, a multicolor printing is performed by superposing inks of three colors. In one of the prior art multicolor printers, the feed of the printing paper is carried out with a platen roller, of which sprocket pins engage with feed holes of the printing paper, and back tension is applied to the printing paper with back tension rollers for preventing color aberration or deviation from predetermined position during both forward and backward feeding.
This prior art multicolor printer has several points to be improved, one of which is that it is rather hard to appropriately adjust peripheral speeds of both the platen roller and the back tension rollers for preventing tearing of peripheries of feed holes, engaging sprocket pins, of the printing paper due to excessive tension in the printing paper.